getlogin_r: return early when linux sentinel value is set

When there is no login uid Linux sets /proc/self/loginid to the sentinel
value of, (uid_t) -1. If this is set we can return early and avoid
needlessly looking up the sentinel value in any configured nss
databases.

Checked on aarch64-linux-gnu.

	* sysdeps/unix/sysv/linux/getlogin_r.c (__getlogin_r_loginuid): Return
	early when linux sentinel value is set.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>

diff --git a/ChangeLog b/ChangeLog
index e6fe2aa1ad46466d8e71afe9f37ae8057573c327..7f2044dee53116116ee3948124f4167027087ea0 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2018-03-27  Jesse Hathaway  <jesse@mbuki-mvuki.org>
+
+       * sysdeps/unix/sysv/linux/getlogin_r.c (__getlogin_r_loginuid): Return
+       early when linux sentinel value is set.
+
 2018-03-27  Samuel Thibault  <samuel.thibault@ens-lyon.org>
 
        * sysdeps/mach/hurd/bits/posix_opt.h (_POSIX_MEMLOCK): Define.

diff --git a/sysdeps/unix/sysv/linux/getlogin_r.c b/sysdeps/unix/sysv/linux/getlogin_r.c
index 73ea14c8f9d257bf0143bf2f3d775fe8f77b9aab..14587712a72ecd0bb1aec4d131f4047a60cc134c 100644 (file)
--- a/sysdeps/unix/sysv/linux/getlogin_r.c
+++ b/sysdeps/unix/sysv/linux/getlogin_r.c
@@ -55,6 +55,15 @@ __getlogin_r_loginuid (char *name, size_t namesize)
          endp == uidbuf || *endp != '\0'))
     return -1;
 
+  /* If there is no login uid, linux sets /proc/self/loginid to the sentinel
+     value of, (uid_t) -1, so check if that value is set and return early to
+     avoid making unneeded nss lookups. */
+  if (uid == (uid_t) -1)
+    {
+      __set_errno (ENXIO);
+      return ENXIO;
+    }
+
   struct passwd pwd;
   struct passwd *tpwd;
   int result = 0;